StarDate

Based on the number of books, movies, and TV shows about it, you might assume that traveling through time is almost as easy as ambling through the park on a sunny day: Just build a TARDIS or soup up your Delorean, and off you go. Alas, the arrow of time moves in only one direction. It allows you to travel into the future, but roadblocks seem to prevent any method that scientists can envision for traveling in the other direction. Wormholes, for example, are theoretical “tunnels” through space and time. They seem to allow travel to other times – past or future. But there’s a problem: The wormhole may collapse as soon as anything enters it – a person, a spaceship, or even a radio beam. Another possibility for traveling into the past is moving really fast. Albert Einstein’s theories of relativity suggest that anything moving faster than light might move backward in time. But any physical object moving at lightspeed would become infinitely massive. That means you’d need an infinite amount of energy just to reach lightspeed – and even more to go faster. A few decades ago, Stephen Hawking suggested that the universe doesn’t like time travel. He wrote that the laws of physics may stop anyone from ever building a time machine – keeping the past safe from its own future. Even so, physics provides some tricks that allow travel to the future, and we’ll have more about that tomorrow. Script by Damond Benningfield

If a cosmic giant sat on a big, gassy planet, it would look a lot like Saturn, the second-largest planet in the solar system. It’s 10 percent wider through its equator than through the poles. But Saturn flattened itself – a result of its low density and fast rotation. Saturn consists of a series of layers. Its core is a dense ball of metal and rock. Around that is a layer of hydrogen that’s squeezed so tightly that it forms a metal. Around that is a layer of liquid hydrogen – the lightest and simplest chemical element. And the planet is topped by an atmosphere that contains methane, ammonia, water, and other compounds. Despite its great size, Saturn spins once every 10.7 hours. That pushes material outward, making the planet fatter through the equator. The combination of its composition and rotation makes Saturn especially light – it’s less dense than water. Saturn doesn’t have a solid surface. But scientists have defined a “surface” as the depth in its atmosphere where the pressure equals the surface pressure on Earth. At that level, Saturn’s gravity is only a bit stronger than Earth’s gravity. So if you were floating at that altitude, you’d feel like you’d added a few pounds. And because of Saturn’s flattened shape, you’d feel heavier at the poles than the equator. Look for Saturn near the Moon tonight. It looks like a bright star to the right of the Moon in early evening, and farther below the Moon at dawn. Script by Damond Benningfield

Building the planets of the solar system was like building a city – it didn’t happen all at once. Instead, it probably took a hundred million years or more to complete the construction project. The first to be completed were Jupiter and Saturn, the Sun’s largest planets. They came together in the prime real estate for planet building – the region with the most raw materials. Closer to the Sun, it was so hot that ices were vaporized and blown away. Farther from the Sun, the material thinned out. But at the distance of Jupiter and Saturn, the balance was just right. The two giants took shape in a hurry. Small grains of ice and rock stuck together to make pebbles, then baseball-sized chunks, then boulders, and so on. That quickly built massive cores, which then swept up huge amounts of leftover hydrogen and helium gas. So within just a few million years, Jupiter and Saturn have grown to monstrous proportions. Uranus and Neptune took shape a little later – within tens of millions of years. Earth and the other rocky inner planets took a bit longer – at least a hundred million years. So the biggest planets of the solar system are also the oldest – dating to shortly after the birth of the Sun. Saturn stands close to the Moon the next couple of nights. The planet looks like a bright star. It’s to the lower left of the Moon as darkness falls tonight, and about the same distance to the right of the Moon tomorrow night. Script by Damond Benningfield

The 41st episode of a celestial series plays out tomorrow: a total lunar eclipse. It’ll be visible around much of the world – but not the Americas. Every eclipse belongs to a series, called a Saros. The eclipses in a Saros are separated by 18 years plus 11 and a third days. If we could watch all the eclipses in the cycle play out, we’d see the Moon pass through Earth’s shadow from top to bottom or bottom to top. So the Moon barely dips its toe in the shadow at the beginning and end of the sequence. But it’s fully immersed during the middle of the cycle, creating total eclipses. And because of that extra third of a day in the cycle, each eclipse occurs a third of the way around the world from the previous one. This eclipse is part of Saros 128. The cycle began in 1304 and will end in 2566 – 71 eclipses in all. Most of Asia and Australia will see this entire eclipse, from beginning to end. And most of the rest of the world will see at least part of it. Totality – when the Moon is completely immersed in the shadow – will last for an hour and 22 minutes. But the eclipse occurs during the middle of the day for those of us in the United States, so we won’t see any of it. What we will see the next couple of nights, though, is a beautiful full Moon – the Fruit Moon or Green Corn Moon – completely free of Earth’s dark shadow. Script by Damond Benningfield

The Moon will briefly cover up the tail of the sea-goat tonight – Deneb Algedi, the brightest star of Capricornus. The sequence will be visible across much of the United States. This vanishing act is an occultation – a type of eclipse in which one object completely covers another. But eclipses are nothing new for Deneb Algedi. Not only does it periodically get covered up by the Moon, but it stages its own eclipses – two of them every day. What we see as Deneb Algedi is a binary – two stars in a tight orbit around each other. The main star in the system is about twice as big and heavy as the Sun, and much brighter. Its companion is a little smaller and fainter than the Sun. We’re looking at the system edge-on, so the stars pass in front of each other – creating eclipses. When the fainter star crosses in front of the brighter one, the system’s overall brightness drops by about 20 percent – enough for a skilled skywatcher to notice. But when the brighter star eclipses the fainter one, the dip is much smaller, so it’s detectable mainly with instruments. The stars orbit each other once a day. That means we see two eclipses per day – just 12 hours apart. Deneb Algedi isn’t especially bright, so it’s hard to see through the bright moonlight. But binoculars will help you pick it out. From much of the western U.S., the Moon will just miss the eclipse-happy tail of the sea-goat. Script by Damond Benningfield

The planet Jupiter will slide past one of the brighter stars of Gemini the next few mornings. At their closest, they’ll be separated by just a fraction of a degree. The star is Wasat – from an Arabic phrase that means “the middle.” But the middle of what has been lost over the centuries. The star also is known as Delta Geminorum – its Bayer designation. The system was devised in the early 17th century by German astronomer Johann Bayer. He named all of the stars in the constellations that were visible from the northern hemisphere. Each star was given a Greek letter followed by the constellation name. If he ran out of letters, he switched to the Latin alphabet. In most constellations, Bayer named the stars in the order of their brightness. The brightest was alpha, the next-brightest was beta, and so on. Sometimes, he ranked the stars on their location or some other system. And he named the stars based on how they looked to the naked eye, so the rankings were completely subjective. So even though delta is the fourth letter in the Greek alphabet, Delta Geminorum is only the eighth-brightest star in Gemini. Jupiter and Wasat are well up in the east at dawn. Jupiter looks like a brilliant star, far to the upper right of even-brighter Venus. Wasat will stand below Jupiter tomorrow. Jupiter will drop past it over the following couple of days, so they’ll be at their closest on Saturday and Sunday. Script by Damond Benningfield

Water is the key ingredient for life on Earth. And as far as we know, it’s a key ingredient for life everywhere else in the universe as well. That shouldn’t be a problem, though, because there’s plenty of water to go around. Water is common in part because it’s made of two of the three most common elements in the universe – hydrogen and oxygen. They come together in the cold of deep space to make grains of ice. Some of those grains are found in the clouds of gas and dust that give birth to new stars and planets. Others form inside those clouds. In recent years, astronomers have found evidence of water in other star systems, and even in other galaxies. They’ve found grains of ice in the disks of material around newborn stars. They’ve seen giant belts of comets, which contain a lot of ice. They’ve discovered water vapor in the atmospheres of a few planets. And they’ve even found evidence that some planets could be covered in oceans of liquid water. One example is TOI 1452 b, which orbits a star that’s much smaller and fainter than the Sun. The planet itself is bigger and heavier than Earth. Given its details and its distance from the star, scientists say it could have a deep global ocean – a possible home for life. TOI 1452 is about a hundred light-years away, in Draco. The dragon twists high across the north at nightfall. But the star is much too faint to see without a telescope. Script by Damond Benningfield

Earth is the only body in the solar system with liquid water on its surface. But it’s not the only one where you can find water. In fact, water is everywhere – from comets and asteroids to the giant planets. Comets and asteroids are chunks of rock, metal, and ices – including water ice. Comets have more ice, but most asteroids probably have large amounts as well. Such bodies might have supplied much of the water on Earth when they collided with our planet billions of years ago. Water ice is common throughout the solar system. It’s been seen at the poles of the Moon and the planet Mercury – the Sun’s closest planet. It forms large polar caps on Mars. And it coats many of the moons of the giant outer planets. Water also has been detected in the clouds of Jupiter and Saturn. And it may be a major component of the outer layers of Uranus and Neptune, the Sun’s most remote planets. To find liquid water, you have to go deep. There may be global oceans of water far below the surfaces of some of the big moons of Jupiter and Saturn, and perhaps some moons of Uranus and Neptune as well. Some of those oceans could hold more water than all of Earth’s oceans combined. On Earth, water is a key ingredient for life. So some of the moons of the outer planets are considered good places to look for life – swimming in oceans of liquid water. We’ll talk about water beyond the solar system tomorrow. Script by Damond Benningfield

Water is all about extremes. The atoms that make up water molecules were forged in some of the hottest environments in the universe. But most of the molecules formed in the cold of deep space. A water molecule consists of two hydrogen atoms plus one oxygen atom – H-2-O. A hydrogen atom contains one electron and one proton. The electrons formed in the first fraction of a second after the Big Bang, when the universe was extremely hot and dense. The protons formed a few minutes later. By about 380,000 years, the universe had expanded and cooled enough for the electrons and protons to stick together to form atoms. And today, hydrogen accounts for more than 90 percent of all the atoms in the universe. Hydrogen and helium, the other major element forged in the Big Bang, soon came together to make stars. And a star’s core is hot enough to “fuse” lighter elements to create heavier ones. The first steps in that process create carbon, nitrogen, and especially oxygen – the third-most abundant element in the universe. When stars die, they expel some of those elements into space. And in the cold away from the stars, hydrogen and oxygen can stick together to make molecules of water. Some of the water’s incorporated into planets – including our own. So the next time you take a cool drink of water, think of the hot-and-cold origins of this important compound. We’ll have more about water tomorrow. Script by Damond Benningfield

To have a strong heart, you naturally need strong arteries. And that’s not a problem for Antares, the heart of the scorpion. It’s flanked by two fairly bright stars that historically have shared a name: Alniyat – an Arabic name that means “the arteries.” The stars probably are siblings of Antares. They all formed from the same giant complex of gas and dust, within the past 10 million years or so. Alniyat I is also known as Sigma Scorpii. It’s a system of four stars. Two of them form a tight pair, with a third close by. The fourth star is farther out. Both stars in the tight grouping are much like Antares. They’re many times the mass of the Sun, so they’ll probably end their lives with titanic explosions. Antares is a little farther along its lifecycle, so it’s closer to that showy demise. Alniyat II is Tau Scorpii. It’s a single star. It, too, is destined to explode as a supernova, but not for several million years – a little later than Antares and the main star of Sigma. On the astronomical clock, though, that’s close – just a few ticks away. Antares and its arteries are close to the right of the Moon at nightfall this evening. Sigma is close to the right or upper right of Antares. Tau is about the same distance to the lower left of Antares. The arteries aren’t as bright as the scorpion’s heart, though, so you might need binoculars to see them through the glare. Script by Damond Benningfield

A spacecraft that’s on it way to Jupiter is “pinballing” around the solar system, getting an extra “kick” as it zips close to the planets. It’ll get the next kick tomorrow, from Venus. The spacecraft is JUICE – Jupiter Icy Moons Explorer. It’s scheduled to arrive at Jupiter in 2031. But it needs help to get there. And it gets that help from the gravity of Venus, Earth, and the Moon. During each encounter, the craft “steals” a bit of gravitational energy. That speeds it up and sculpts its path around the Sun. The encounters drastically reduce the amount of fuel JUICE must carry, cutting its size and weight and reducing its cost. JUICE flew past Earth and the Moon a year ago. It’ll get additional boosts from Earth in 2026 and ’29. JUICE will scan Venus as it flies past. That will give scientists some extra information about the planet. And it’ll give engineers a chance to check out the craft’s instruments. When JUICE arrives at Jupiter, it’ll orbit the planet for almost three years. After that, it’ll begin orbiting the planet’s largest moon, Ganymede. Its observations of Ganymede and Jupiter’s other icy moons will reveal details about their possible buried oceans, which could be habitats for microscopic life. Venus and Jupiter are in the dawn sky now. Venus is the brilliant “morning star,” with slightly fainter Jupiter to its upper right – two destinations for a “pinballing” explorer. Script by Damond Benningfield

Only a few of the thousands of known planets in other star systems have ever been seen. Most exoplanets are discovered through their effects on their parent stars. But a system in Pegasus is a major exception. Astronomers have discovered four planets in the system – and they’ve seen all of them. HR 8799 is about 130 light-years from Earth. The star is bigger, brighter, and heavier than the Sun. And it’s much younger – tens of millions of years, versus four and a half billion years for the Sun. And that’s one reason we can see the planets – they’re still warm from their birth, so they produce a lot of infrared light. Another reason we can see the planets is that they’re a long way out from the star – many times the distance from Earth to the Sun – so they’re not masked by the star’s light. And the planets are giants – they’re up to 10 times the mass of Jupiter, the giant of our own solar system. Recent observations by Webb Space Telescope suggest the planets formed in the same way as Jupiter. Blobs of rock and metal stuck together to form a heavy core. The gravity of the core then swept up huge amounts of gas. The system might still be taking shape. A giant disk of dust surrounds the planets, and is being stirred up by their gravity. And the planets themselves may be shifting position – finding the right arrangement before this young, busy system settles down. Script by Damond Benningfield

A recently discovered planet is facing its final days. It’s evaporating, leaving a trail of debris that stretches halfway along its orbit. The planet is known by a catalog number – BD +05 4868 Ab. It’s only the fourth evaporating planet ever seen. It orbits the main star in a binary system in Pegasus, which is in the eastern sky at nightfall. The star is smaller and fainter than the Sun, and more than twice the age of the Sun. The planet was discovered by TESS, a planet-hunting space telescope. The planet passes in front of its parent star once every 30.5-hour orbit, blocking some of the star’s light. But the dips in starlight are ragged and look different from orbit to orbit. That suggests the planet is shedding material, forming a lumpy trail. The planet is small, and it orbits the star at just two percent of the distance from Earth to the Sun. At that range, it’s heated to 3,000 degrees Fahrenheit. That vaporizes minerals at the surface. The vapor boils into space, where it cools and condenses to form solid grains. That creates a thick trail that extends both behind and ahead of the planet. As more of the planet vaporizes, its gravity weakens, allowing even more material to escape. So the planet could vanish entirely in as little as a million years. Astronomers will look at the system with Webb Space Telescope – revealing more details about this vanishing planet. Script by Damond Benningfield

The Sun isn’t bothered by much. That’s because it travels through the Milky Way on its own. But most of the stars in the galaxy have at least one companion star. And the interactions between them can have a big impact. Consider Spica, a bright star near the Moon tonight. Although it looks like a single star, it’s really at least two stars. One of them is more than 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. That makes Spica one of the more impressive binary systems around. The stars are extremely close together. They follow a stretched-out orbit that brings their surfaces to within about 10 million miles of each other. So the stars have big effects on each other. For one thing, their mutual gravitational pull distorts both stars. They’re shaped like eggs, with the tapered end pointing toward the other star. Also, the pull of the smaller star appears to create ripples in the larger one. And the tapered end of each star is hotter than its opposite hemisphere. In a few million years, the larger star will explode as a supernova. That’s likely to blast away some of the gas at the surface of the companion. And it’ll probably send the smaller star zipping across the galaxy – fired into space by a close companion. Look for Spica to the right of the Moon early this evening. The fainter planet Mars is farther to the lower right of the Moon. Script by Damond Benningfield

Mars is dry, cold, and quiet. But that hasn’t always been the case. Billions of years ago it was much busier – and perhaps a comfortable home for life. Mars has had three major geological ages. The oldest was the Noachian. It’s named for a large highlands region in the southern hemisphere. It began about 4.1 billion years ago, and lasted for 400 million years. The solar system was still packed with big “leftovers” from the birth of the planets then. Many of them slammed into Mars, forming wide basins that are still visible today. At the same time, giant volcanoes belched gases into the atmosphere. That trapped heat, making Mars much warmer. Clouds might have produced rain or snow. The precipitation carved rivers and filled lakes and maybe even a large ocean. Conditions could have allowed the formation of microscopic life. At the end of that period, there were fewer impacts and less volcanic activity. Mars cooled off, and the water dried up. So Mars became quieter as the Noachian Age ended, and the next age began. Mars is close to the right or upper right of the Moon early this evening. It looks like a fairly bright star. But it’s quite low in the sky, especially as seen from the northern half of the country, so you need a clear horizon to spot it. The star Spica, which is about twice as bright as Mars, stands to the upper left of the Moon. We’ll have more about Spica tomorrow. Script by Damond Benningfield

Every pilot knows to check the weather before takeoff – no one wants to fly into a storm. And in the future, they might want to check the space weather as well. Storms on the Sun can interfere with technology here on Earth – including aviation technology. Solar storms are giant explosions of energy and charged particles. When these outbursts hit Earth, the effects can range from damaged satellites to power blackouts on the ground. Some radio frequencies can be blacked out as well. Scientists recently looked at the impacts on aviation. They studied tracking information for three small aircraft recorded during a massive solar flare in February of 2024. The aircraft automatically reported their position and other details to air traffic control and to other aircraft. The position information came from GPS satellites. But several times during the solar storm, the aircraft briefly lost touch, or they received bad position information. The problems were brief. But future storms could cause bigger problems. Bad information from GPS satellites, drops in radio links, and even radar blackouts could force flight controllers to rely on older methods to keep planes and passengers safe. That could cause delays and backups – or worse. So the researchers suggested that space weather briefings be developed for pilots – helping them safely navigate through space weather. Script by Damond Benningfield

As Earth was thawing out at the end of the last ice age, it was hit by a powerful blast from the Sun. The storm would have triggered spectacular displays of the northern and southern lights. And it left an imprint in tree rings. Using that imprint, scientists have found that the storm was the most powerful yet recorded. And they even have a time for the event: the first quarter of the year 12,350 BC. Solar storms pelt Earth all the time. Most of the storms are small. But big ones can damage or destroy satellites, zap power systems on the ground, and cause other mischief. The biggest one ever seen took place in 1859. It knocked out telegraph systems around the world. But scientists have found evidence of even bigger events in the more-distant past. Some of the events are recorded in tree rings. Charged particles from the storms interact with Earth’s atmosphere to produce a radioactive form of carbon. Trees take up some of the carbon, which decays to a more stable form at a known rate. So comparing the ratio of carbon isotopes in tree rings can tell us when big storms took place. Researchers measured the carbon in rings from the end of the ice age. And they developed a new model of chemistry of the atmosphere during such cold periods. Their work showed that Earth was hit by the strongest solar storm yet discovered more than 14,000 years ago. More about space weather tomorrow. Script by Damond Benningfield

If you watch the stars on a dark night, it’s easy to think of the sky as a great dome. But as the night goes on, the dome rotates. New stars rise in the east, while others disappear in the west. So ancient skywatchers thought of the sky not as a dome, but a sphere that completely encircles us – the celestial sphere. To the Greeks, the sphere was real – a perfect crystalline surface, with the stars hanging from it like lanterns. Earth stood still at the middle of the sphere, which turned around it. Today, of course, we know that Earth is turning, and the stars are so far away that they appear to be fixed in place. Yet astronomers still use the celestial sphere. Their coordinate system is based on it. The system has lines of latitude and longitude, an equator, and north and south poles – all of which are projections of Earth’s coordinates. The celestial poles, for example, are based on the projection of Earth’s poles – the directions in which our planet’s axis is pointing. There’s also a celestial equator – an extension of Earth’s equator. As darkness falls tonight, it arcs from Aquarius, in the east; through Aquila, in the south; and down to Virgo, in the west. Only those who live near the equator can see the entire celestial sphere. For everyone else, it’s clipped. And at the poles, only half of the sphere is ever visible – a great dome showing the same stars all year long. Script by Damond Benningfield

Many “open” star clusters arch high overhead on summer nights. They’re lined up along the glowing band of the Milky Way – the outline of our home galaxy. Each cluster is a family of stars – from a few dozen to a thousand or more. But open clusters don’t stay together for long. Their stars eventually spread out, so the cluster disappears. Some families begin to spread out early – before many of their stars are even fully formed. One recently discovered example is called Ophion. It consists of more than a thousand stars. Astronomers found the group by analyzing data from Gaia, a space telescope. They looked through observations of more than 200 million stars. Then they narrowed their search to stars that are cooler than the Sun, and no more than 20 million years old. And Ophion just popped out. The stars form a giant clump that’s centered about 650 light-years away. But all of its members are going their own way. So they don’t form an obvious “cluster” – a tight grouping that’s easy to pick out. Ophion is on the edge of a region that’s given birth to many thousands of stars. Exploding stars in that region – or within Ophion itself – might have scattered the stars like bowling pins, keeping the family from sticking together. Ophion is near the middle of Ophiuchus, which is well up in the south-southwest at nightfall. You can see many clusters there – but not a hint of the ill-fated Ophion. Script by Damond Benningfield

Human eyes are perfectly tuned to see sunlight. But that’s a thin slice of the total range of light. As a result, we miss a lot of what’s out there – even objects that are big and close. A recently discovered example is a cloud of gas and dust that’s been named Eos. It spans about 40 times the width of the Moon. But it’s thinly spread, and it produces most of its light in the far-ultraviolet – wavelengths we can’t see. And even if we could see them, Earth’s atmosphere blocks them. So Eos wasn’t discovered until astronomers combed through observations made two decades ago by a Korean space telescope. The cloud’s inner edge is about 300 light-years away. It’s along the rim of the Local Bubble – a giant void around the solar system that’s been cleared out by exploding stars. Eos is about 170 light-years across. It contains enough gas to make more than 5,000 stars as heavy as the Sun. But there’s no evidence that it’s ever given birth to any stars at all. And while it could spawn stars in the future, that’s not likely. The cloud is evaporating, and should vanish in about six million years. Eos is centered along the border between the northern crown and the head of the serpent. That point is high in the west-southwest at nightfall, to the upper left of the bright star Arcturus. But unless you have your own space telescope, there’s no way to see this giant neighbor. Script by Damond Benningfield